Chopper



patenteci Sept. 9, 1952 UNITED STATES PATENT OFFICE CHOPPER v Curtiss R. Schafer, Ridgefield, Conn. Application September 3, 1949, Serial N 0. 114,055

,1 The present invention relates to choppers, switching devices intended for interrupting the fiow of current of low level, as is requiredin the amplification thereof to a more readily useful level. Usuallly the current is direct, or it may be slowly varying or alternating current that is herein treated as direct current because the rate of variation is so low as to require conversion to interrupted or alternating current of a frequency high enough to be readily amplified. The need for measuring very low voltages is met in various types of test and control equipment. Some form of circuit interrupter or chopper is commonly connected to the source of voltage to be measured, enabling the use of an amplifier designed for alternating current or interrupted unidirectional signals. Commutators and vibrating contacts have been used for this purpose. For especially low-level measurements, however, disturbances or noise of uncertain character are introduced. Anobject of this inventionis to enable the utilization of particularly small voltages by a chopper of reduced noise characteristics.

."I haveconsidered a factor in the noise to be the result of motion of chopper parts, through the earth's magnetic field and through stray magnetic fields such as those set up by the chopper-driving means itself. Spuriouspotentials', induced by motion of the contacts and metallic contact-supporting and circuit struc tures through the ambient magnetic field are eliminated in the embodiment described in detail below by enclosing the moving metallic parts in a shield of magnetic material. v

Stray. fields are inherently associated with the actuatoizlwhether electro-mechanical or even purely mechanical. I have found the proximity of the actuator to the chopper contacts to be a significant cause of noise. The embodiment below employs a nonmetallic transmission between the actuator and the movable contact. Advantageously a fiuid line where only the fluid moves in the vicinity of the contacts is used, having particularly low inertia and a negligeable dielectric constant in the case of air, and being generally free of mechanical transient vibration effects inherent with solid transmission links,

An illustrative form of the invention is shown in the single figure of the accompanying drawing. Contacts and I2 of silver or other low contact-resistance metal are enclosed in a case or shielding structure I 4 of magnetic and electrically conductive material, conveniently soft iron that is solid or laminated. Stray varying 5 Claims. (01. 200-87) magnetic fields will harmlessly induce currents in the case; and ambient magnetic fields will be shunted about the contacts to be ineffectual in respect to the contacts when in motion. Contact I0 is carried on a metal arm I6 supported by insulating block 18, and has a lead 20 to external terminal 22 that extends through insulating bushing 24 in a small hole in the case. Adjusting screw 26, having a tip 28 of insulating material, enables convenient setting of stationary contact ID from outside the case. Arm I 6 is of leafspring stock as of beryllium copper, and is biased against screw tip 28.

Movable contact I2 is at once supported by diaphragm 30 and electrically connected by that diaphragm to the shielding structure M which thus constitutes the second terminal of the device. The diaphragm is secured by clamping ring 3.2 and spacing rin 34 in an air-tight connection to the inside of the shielding structure, opposite aperture 36 therein. The diaphragm thus divides the shielding structure into two compartments A and B. Pressure against the diaphragm applied via aperture 36 in the shield tends to compress the air in compartment B. The pressure changes that are gradual, over a long period, can be minimized by an appropriately small hole 38, communicating to the atmosphere. The confined space is of advantage due to the elasticity of the air that facilitates high chopping rates. I

A cap 40 as of aluminum is secured to the iron case l4. Cap 40 has a small hole 42 bored through it. This hole and hole 38 tend to prevent the build-up of unbalanced pressures on the diaphragm that might keep the contacts permanently open or closed.

A line of tubing 44 (of metal or insulation) provides a confined air passage through aperture 36 for a column of air to operate or drive the diaphragm in a vibratory motion. The air column is energized by actuator 46 that takes the form of a moving-coil speaker having a. diaphragm that is of the same air-tight construction as diaphragm 30. Actuator 46 includes coil 50 on the diaphragm and stationary permanent magnet 52, and is energized from an alternating current source (not shown) of frequency corresponding to the desired chopping frequency. One thousand cycles per second is illustrative. This particular type of actuator is effective in both strokes, toward and away from circuit-closing position. Because it does not require a stiff spring for a return stroke, the amount of energy required is comparatively small, and the actuabe provided. Other changes in detail will no doubt occur to those skilled in the art, as will other applications of the novel device.

Con

4. A circuit interrupter including a shield of magnetic material, a pair of contacts enclosed in said shield, one of said contacts being movable in relation to the other, said one contact being supported by a diaphragm, a length of tubing having one end fluid-coupled to said diaphragm, a second diaphragm fluid-coupled to the opposite end of said tubing, a coil attached to said second diaphragm, and means for establishing a con- :stant magnetic field for-said coil, saidftub'ing, said 'coil,'said second "diaphragm and said-magnetic field means being situated external of said mag- ;netic shield, whereby electrical excitation of said coil at any desired frequency will operate said sequerrtly it is appropriate that the amoended claims be accorded that broad interpretation that is consistent with the spirit and scope of the invention. a

What is claimed is:

1. A chopper for converting direct current of low level into intermittent current to facilitate amplification, including a stationary contact and a movablymounted contact, a shielding structure of magnetic material substantially enclosing said contacts, an electromechanical vibratory actuating device ex-ternal of said shielding structure, and means transmitting actuating stress from said. actuating device to said movably mounted contact, said means including electrical insulating material penetrating said Shield. 7

2. A chopper for converting direct currentof low level into intermittent current to facilitate amplification, including a stationary contact and a movable contact, a shielding structure of magnetic material substantially enclosing said contacts but provided with an aperture, an electromechanical vibrator external of said shield, and an air-tight diaphragm carrying said movable contact and dividing said shielding structure into two compartments one of which communicates to said aperture, the other of said compartments having a fluid pressure transmitting line connected to said vibrator.

3. A chopper for converting direct current of low level into intermittent current to facilitate amplification including a pair of relatively movable contacts, an, electromechanicalsvibratory actuator, a tube providing a fluid transmission contacts via the electrically isolating fluid cou- ,pling afiorded by said diaphragms and said tubing, and whereby said moving contact is protected against induction of spurious potentials therein while in motion Which would otherwise occur due to the ambient magnetic field including that produced by the coil and the magnetic field means.

' 5. Achopper for converting direct current of low level into intermittentv current to facilitate amplification, including a pair of switch contacts, an electromechanical vibrator, a magnetic shield enclosing said switch contacts but ex,- cluding said vibrator, and vibration transmission means interconnecting said vibrator and one of said switch contacts and reciprocably penetrating saidi shield, said transmission, means including column interposed between said actuator and an-electrical insulating portion between said vibrator and said one switch contact.

The following references are of record in the file of this patentz UNITED STATES PATENT Number Name Date 821,992 DoWns May 29, 1906 1,628,723 Hall May 17, 1927 1,689,121 Ferd'on Oct.23 1928 1,836,058 Bancroft an; Dec. 15 1931 2,109,761 Warnke Mar. 1,1938 2,114,036 Smith et al. 'Apr. 12,,1938 2,183,612 Gub in Dec. 19,1939 2,197,47& Jackson et al. Apr. 16, 1946 2,217,177 Massa Oct. 8, 1940 2,280443 Dann -4.-- Apr. 21,1942 2143 42 Buttrey Apr. 6,..1948.

.. FOREIGN PATENTS .umber country fDat'e I 29,891 Denmark June 23; 1920 353,634;-

Great Britain Oct. 15, I931, 

